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SubjectRe: Patch for route.c
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"Richard B. Johnson" <root@analogic.com> writes:
> [SNIPPED]
> Just a note. If you do NOT have two or more different network paths into
> or out of your machine (like two Ethernet cards, etc), you do NOT want
> to run `gated`. For some strange reason, it runs by default on Sun machines.
> There is no way that a machine with a single connection to a network can
> provide a "route" to something on the same wire. To provide such a
> "route" results in a large amount of extra traffic because the packets are
> duplicated.

This is nonsense. We run gated on many machines with a single
interface, because it we have multiple exit points from the ethernet
it's on. Gated means that the packet will only travel once over the
ethernet instead of having to bounce of one of the exit routers.

> When `gated` runs, it advertises that it can provide a route to everything
> that it can see, i.e., the local network and the default route (perhaps
> to the internet through a Cisco router, etc.). Other machines running

No. If gated is incorrectly setup, it may advertise a default route
etc etc. This is dependant on the gated config, and the routing
protocol in question being run.

> `gated` will change their routing to send packets to the machine that
> magically declares that it has such a route, EVEN THOUGH THESE MACHINES
> ALREADY HAVE THE SAME STATIC ROUTE! The result is that packets will

This is part of the problem. Gated will only deal with the routes it
knows about. If you haven't told gated about all the magic static
routes you've included, then it may very well get it wrong. But this
is purely a misconfiguration issue, and nothing to do with gated as
such.

> You should have static routes set up to handle traffic on a single wire
> if you have only a single wire!

And what if that single wire is a transit link? this ethernet is
joining two large networks, and there's a server on that ethernet?
then it needs routes for all the subnets in each network.

> Since `traceroute` only uses IP addresses, not Ethernet hardware addresses,
> everything looks fine with traceroute because the IP addresses don't
> change during the duplicate routing. You need to use a Network Analyzer,
> or Sun's snoop to see what is happening. You will see the same packets
> duplicated with different hardware addresses.

This is nonsense. Traceroute will show you the ip number of each
hop. If the packet isn't being routed through a machine, it won't show
on traceroute, but if it IS routed (i.e. because gated is incorrectly
configured), then it WILL show on the traceroute.

> We have 600+ nodes here, many of them are Suns. We were having problems
> with massive LAN congestion until we reconfigured all the Suns to NOT
> run `gated`. The result was a reduction in traffic to less than 1 percent
> (yes, 1/100th) of the original overloaded condition.

No doubt it fixed it, but I'd take another looking at your reasons for
thinking why it fixed it.

Michael.

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